HEROIN causes the most harm to Scottish society despite the nation's appalling relationship with alcohol, according to a new study ranking the harm posed by drugs.

A survey of drugs specialists also found cannabis was considered the least dangerous substance, although it is labelled as a class B drug.

The top 10 of the drugs considered most dangerous, taking into account harm to both individual users and society, included four Class A drugs, two class B and one class C. Three legal substances were also included, with alcohol ranked fourth, solvents in fifth place and tobacco ranked sixth. However, ecstasy and magic mushrooms – both class A drugs – were perceived as among the least harmful.

Lead author Dr Mark Taylor, an Edinburgh-based consultant psychiatrist, said the research aimed to try to shed some "perspective" on the drugs issue.

"We wanted to capture the various domains of harm, which we reduced to the categories of harm to self and harm to others – ie harm to society," he said. "We then wanted to get a sense – according to the addiction experts – of rankings relative to other substances.

"There is a whole debate about safety versus legality. Alcohol is clearly the drug of choice for our society but it is not without dangers."

The research, published by online medical journal BMJ Open, surveyed nearly 300 clinical experts from across Scotland, including psychiatrists, social workers, addiction nurses and GPs on their views on the harms of substances. Participants scored each substance from zero – no risk – to three – extreme risk – on nine different measures.

To assess the "social harm" of a drug, issues such as the costs to the NHS, violent behaviour, neglect of children and financial problems were taken into account.

Taylor, who holds honorary senior lecturer posts at both Edinburgh and Glasgow universities, said the study aimed to reproduce previous work led by former chief drugs adviser to the UK Government, Professor David Nutt – who sparked controversy after publishing a drugs harm ranking list five years ago.

Nutt was sacked from his position as chair of the Advisory Council on Misuse of Drugs in 2009 after clashing with MPs over claims that alcohol and tobacco were more harmful than many illegal drugs, including ecstasy and cannabis.

He also suggested taking ecstasy was no more dangerous than riding a horse.

Taylor said the Scottish research involved a larger number of experts than previous studies, and one surprising finding was how "benign" cannabis was perceived to be.

One factor may be high potency cannabis was not in widespread use at the time of the survey. But Taylor added the experts surveyed – who all work in addiction services – may also not see many people who have a problem with the drug.

"As a general adult psychiatrist, I see quite a few people who have come to grief due to excessive cannabis use, often related to precipitating a psychotic illness or paranoid illness," he said. "The addiction experts don't see that so much, as cannabis addicts often don't seek help. Nevertheless, we were surprised at how low the cannabis ranking was and also the ecstasy ranking to a certain extent, considering it is a class A controlled drug."

The study suggests that a new method for ranking drug harm – separate from that used in the criminal justice system – should be introduce to help guide health policies.

It concluded: "Increasing public awareness of the potential for harm of all the drugs examined whether legal or illegal and finding ways of reducing the demand for psychoactive substances should be the focus rather than imposing harsh penalties for their use."

Dr Evelyn Gillan, chief executive of Alcohol Focus Scotland, pointed out alcohol was the only drug which ranked more highly for social harm than personal harm in the study.

"The impact of alcohol's harm to people other than the drinker comes in many forms, ranging from problems with family members and friends to strangers in the street," she said.

"Despite the devastating effect of alcohol on people's lives, drinking and drinking to excess is viewed as normal behaviour in our society, while drug use is generally viewed as more risky and problematic."

However, Gavin Partington of the Wine and Spirit Trade Association said: "This study appears designed to support the view of a minority who wrongly seek to equate alcohol with harmful illegal drugs. It is not a view shared by the vast majority of Scots who enjoy drinking in moderation."

Inspector Tommy Crombie, national drugs co-ordinator for the Scottish Crime and Drug Enforcement Agency, said all kinds of substance misuse posed risks to users and placed significant costs on justice, health and social systems.

"Those who are tempted to use illegal drugs should be under no doubt these substances are harmful and can cause serious health implications," he said. "Cannabis, for example, remains the most widely misused illicit drug in Scotland and evidence does exist to show that the drug is harmful, particularly stronger strains."

That view was backed by Marjorie Wallace, chief executive of mental health charity, SANE.

She said: "We receive daily evidence that the long-term use of 'skunk' cannabis can trigger frightening psychotic episodes, causes relapse and may bring about severe mental illnesses such as schizophrenia."